Vitreous enamel frit



Headsets Pater O VITREOUS ENAMEL FRIT Lewis C. Hoffman, Scotch Plains, N.J., assignor to El.

. du Pont de Nemours and Company, Wilmington,.Del.,

a corporation of Delaware No Drawing. Application February Serial No. 791,291

8 Claims. (Cl. 117-70) This invention relates to a new and improved vitreous enamel fnit. perature maturing enamel enamelling of steel. Most commercial enamel frits for steel require firing at 1500 -F. In recent years attempts havebeen made to develop frit compositions that may be fired at lower temperatures, but the properties of these frits have not been satisfactory for commercial practice. The frits of hit suitable for use in the the present invention have overcome the deficiencies of previously developed low temperature firing steel enamels. Firing of vitreous enamel hits at atemperature under 1100 F. will avoid sagging of steel allowing the use'of thinner gage metal. The oxidation of the steel is considerably reduced avoiding the necessity of thick enamel coatings to dissolve the oxide formed. No hydrogen is evolved during firing and the problems of blistering and reboiling are avoided. The use of thin enamel coatings permits greater flexibility and impact without damage to the enamel. Moisture in the enamel frit slips does not react with carbon at low temperature thus minimizing gas evolving reactions so often observed and allowing the use of steel with higher carbon content than is possible with high temperature maturing enamels.

It is therefore an object of this invention to provide a low temperature maturing frit suitable for use in the enamelling of steel and iron.

More particularly, it relates to a low tem- The ratio I and. the sum of B 0 R20, PhD and F =52-58 mol percent. I 1 I v The cover coat should contain the following constitu ents in the ranges and proportions,

Throughout the specification and claims, the term R 0 refers to alkali metal oxide, Na O, K 0, or Li O.

The ground coat of this invention may be covered by other cover coats: than those herein specified and the cover'coats'of this invention may be placed on other ground coats to good advantage, however, it is preferred, in order to obtain optimum results to use both the ground and cover coats of this'invention in the enamelling of iron or steel.

f The specific ranges and proportions of the constituents of the enamel frits of this invention permit the-use of 'relatively.. high alkali content and relatively low silica content in comparisonto former steel enamels and thus It is a further object of this invention to provide a new type of steel enamel. 7

It is another object of this invention to provide a steel enamel fr-it which may be applied to iron or steel and fired at a temperature between 490 and 690 C. to pro;

duce a satisfactory vitreous enamel coating.

Other objects of the invention will appear hereinafter.

NIB. order that the objects of this invention may be. accomplished and in order that the enamel coatings adhere tightly to iron or steel which, in general, has a linear coefficient of thermal expansion between 120 and 140x 10-", the fri-t composition must contain the following ingredients in certain ranges and proportions as follows:

The ground coat should contain the following constituents in the ranges and proportions,

obtain lower firing temperature enamels having equal chemical resistance or better chemical resistance at equal firing temperature. The hits of this invention are particularly advantageous for use on enamelers iron, cast iron, ordinary cold rolled or hot rolled steel and Wrought iron, which ferrous materials have a linear expansion coefficient of between 120 and l40 10-".

- Two types of hit are generally required for the enamelling of iron and steel.

Ground or base coat frits had to have slightly lower or matching linear thermal expansion coeificients to the substrate metal to prevent cracking on cooling after firing;

a wide maturing temperature range because they are commonly subjected to one or more than one firing and smallamounts of melted in C00, NiO, and Mn0 for b'est adherence to the substrate metal. I

Cover coats require less strict matchingof thermal expansion coefiicients. They may be used if their coefficients are 10 10- units'of the substrate metal.

f They must have the same broad maturing range as the Mol percent SiO 27-30 B 0 I 22-28 TiO 7-12 N21 O 16-23 K 0 0.5-3 Li O 5-12 BaO 0-4 Sbg03 v C00 1 0-2 I NiO '0-1 MnO; 0-1 BbO I 0-2 F: 0-5

ground coat trits and additionally a low tendency to crystallize on cooling because they are commonly cooled more slowly than the ground coats. Primarily they must have very high chemical resistance and a pleasing, glossy surface.

The frits of this invention are made by melting to- I gether oxides, carbonates, nitrates or sulfates of the indicated ingredients. No differences were seen in the frit properties starting from difierent compounds. provided equivalent amounts were used. For example,

.Patented Mar. 29, 1960 3 fluorine can be introduced as NaF, NH F, NzSiFe, or PbF with equivalent results provided the remainder of the composition is adjusted for the introduced cations. The melting was carried out at 1000l300 C. and when gas evolution and reaction ceased the molten glass was discharged into water or through water cooled rolls to form the frit.

In accordance with conventional practice steel or iron requires a surface preparation prior to enamelling. The following process will suitably prepare the surface of iron or steel for enamelling:

(l) Immerse metal in hot chromic acid-sulfuric acid mixture. 7

(2) Rinse with tap water.

(3) Immerse in 7% H 80 at 70 C. for five minutes to deoxidize. I a a (4) Rinse with tap water.

(5) Dip metal in nickel sulfate solution to aid adherence; -3 oz. per gal. NiSO, (pH=3); clip for minutes at 70-80 C.

(6) Rinse with tap water.

(7) Neutralize in 1 oz. per gal. NaOH at room temperature.

(8) Rinse with tap water.

(9) Dry thoroughly.

The frit is incorporated in a slip for application to an iron or steel surface by comminution in a ball or pebble mill with the addition of a suitable vehicle, water,

pigments and possibly other addition agents. A small amount of methyl or ethyl alcohol, glycol or other water-soluble organic compound may be added to the mill batch to increase or decrease the drying rate of the resulting slip. Anti-tearing agents may be added to the slip to minimize adhesion failures in the heating-up stage of firing, however, in general such agents are not essential. As anti-tearing agents may be mentioned the alkali metaborate-alkali silicate mixtures of Dayrup Patent No. 2,653,877, borax, sodium silicate, urea and NaF. Setting-up agents to promote fast elimination of fluidity upon drying coated surface, for example, bentonite may also be added. As coloring pigments metal oxides, for example, T10 cobalt aluminate ZrO iron oxide, cadmium sulfaselenide and the like may be added as mill addition agents. The slips are applied to the iron or steel, or in the case of cover coats on the ground coat of enamel, by dipping, brushing, painting, spraying or in any other desired manner. After application of the slip, the coated pieces are dried, either at room temperature or in a drying oven at a temperature of to C. The dried pieces are then placed in a suitable firing furnace (lehr) and fired for sufiicient time to develop optimum gloss (2-60 min. at 490690 C.)

The following examples are given to illustrate certain preferred enamel ground coat and cover coat compositions and preferred methods of operation. These examples are. not to be considered as limiting the invention to the details therein set forth.

Nine examples of suitable ground coat fn'ts of this invention are tabulated as Examples 1 to 9, inclusive in Tables I and II below, Table I giving the percentages of constituents in mol percent and Table II in weight percent.

TABLE I Ground coats, mol percent Example No 1 2 3 4 5 6 7 8 9 i a 2 i 1 9 R2O+Pb0 1.56 1.61 1. 02 1.52 1. 5. 1.66 1. 4a 1.81 1.65 Sum of: B101, R20, PbO and TABLE II Ground coats, weight percent Example No 1 2 3 4 5 6 7 8 9 F: "2. 1.8 2.3 2.3 1.8 Sum of: B101, R10,,Pb0 and maturing between 490 C. and 690 C. having the following composition:

and the sum of B R 0, PhD and F =52-58 mol percent, firing said frit at the maturing temperature percent, and firing said frit at the maturing temperature thereof.

3. The method of enamelling iron and steel with an enamel cover coat which comprises applying over a ground coat enamel on said metal a cover coat fn't maturing between 490 C. and 690 C. and having the composition:

Mol percent SiO 23-32 B;O 7-23 T10 13-22 Na O 15-22 K 0 1-7 Li O 8-12 BaO 0-6 Sb O 0-1 Z110 0-5 PbO 0-5 CdO 0-2 2 0-6 in which the ratio thereof, applying over said fired ground coat, a cover coat frit, maturing between 490 C. and 690 C. having the following composition:

Mol percent SiO 23-32 B 0 7-23 "n0 13-22 N320 K 0 1-7 Li O 8-12 BaO 0-6 813203 0-1 ZnO 0-5 PbO 0-5 CdO 0-2 F 0-6 in which SiO l-ZTiO RzO'PPbO 1.4 to 2.3

and the sum of B 0 R 0, PbO and F =46-60 mol percent, and firing said cover coat frit at the maturing temperature thereof. 2. The method of enamelling iron or steel with an enamel ground coat which comprises applying to said metal surface a ground coat frit maturing between 490 C, and 690 C. having the composition:

Mol percent SiO 27-30 B 0 22-28 Ti0 7-12 Na O 16-23 K 0 0.5-3.0 Li O 5-12 BaO 0-4 Sb O 0-1 C00 0-2 NiO 0-1 MnO 0-1 PbO 0-2 F O-5 in which the ratio SiO -l-2TiO R2Q+PbO -1.4 to 1.9

and the sum of B303, R20, PhD and F3=52-58 mol SiO2+2TiO R2O+Pb0 -1.4 to 2.3

and the sum of B 0 PbO and F =46-60 mol percent,

and firing said frit at the maturing temperature thereof. 4. Vitreous enamelled iron or steel comprising an iron or steel surface having an enamel ground coat comprising the following composition:

and the sum of B 0 R 0, PbO and F =52-58 mol percent, and an enamel cover coat comprising the following composition:

Mol percent SiO 23-32 B 0 7-23 TiO 13-22 Na O 15-22 K 0 1-7 Li O 8-12 13:10 O-6 Sb O 0-1 ZnO 0-5 PbO 0-5 CdO 0-2 F O-i in which the ratio n t e sum of B 0 PhD and F =46-6O mol percent.

5. Vitreous enamelled iron or steel comprising an iron or steel surface having an enamel ground coat comprising the following composition:

and the sum of B R 0, PhD and F =52-58 mol percent.

6. Vitreous enamelled iron or steel comprising an iron or steel surface having an enamel ground coat and an enamel cover coat comprising the following composition:

M01 percent SiO 23-32 B 0 7-23 Ti0 13-22 Na 0 15-22 K 0 1-7 Li O 8-12 BaO 0-6 Sb O 0-1 ZnO 0-5 PbO 0-5 CdO 0-2 F 0-6 V in which the ratio W- 1.4; to

and the sum of B 0 PbO and F =46-60 mol percent.

7. A vitreous ground coat frit having a maturing temperature between 490 C. and 690 C. which will adhere to iron or steel having a linear coeflicient of thermal expansion below 140x 10- which comprises M01 percent SiO 27-30 B 0 22-28 Ti0 7-12 Na O 16-23 K 0 0.5-3.0 Li O 5-12 BaO 0-4 Sb O 0-1 CoO 0-2 NiO 0-1 M1102 PbO 0-2 F 0-5 in which the ratio SiO +2TiO W1.4 to 1.9

and the sum of B 0 R 0, PbO and F =52-58 mol percent.

8. A vitreous cover coat frit having a maturing temperature between 490 C. and 690 C. which will adhere to a vitreous enamel ground coat on iron or steel having a linear coeflicient of thermal expansion below x10 andthe sum of B203, PhD and F2=46-60 mol percent.

References Cited in the file of this patent UNITED STATES PATENTS 2,467,114 Dayrup Apr. 12, 1949 2,642,364 Beatty et al June 16, 1953 2,660,531 Fraser et a1 Nov. 24, 1953 2,702,762 Chester Feb. 22, 1955 2,842,458 Fenney et a1 July 8, 1958 

1. THE METHOD OF ENAMELLING IRON OR STEEL WHICH COMPRISES APPLYING TO SAID METAL SURFACE A GROUND COAT FRIT, MATURING BETWEEN 490*C. AND 690*C. HAVING THE FOLLOWING COMPOSITION: MOL PERCENT SIO2 27-30 B2O3 22-28 TIO2 7-12 NA2O 16-23 K2O 0.5-3.0 LI2O 5-12 BAO 0-4 SB2O3 0-1 C0O 0-2 NIO 0-1 MNO2 0-1 PHO 0-2 F2 0-5 IN WHICH THE RATIO 